1. Field
Exemplary embodiments of the present invention relate to semiconductor design technology, and more particularly, to a semiconductor memory and a memory system for tuning a clock-based parameter.
2. Description of the Related Art
AC parameters relating to a semiconductor memory may be varied by controlling the internal/external environments of the semiconductor memory. Lots of testing and tuning works are required for a memory controller to check and optimize the AC parameters.
For example, an AC parameter ‘tDQSCK’ indicates a timing difference between a system clock used in a semiconductor memory and a data strobe signal output from the semiconductor memory when a read operation is performed and indicates the degree of an alignment of the data strobe signal and the system clock. The timing of the data strobe signal is determined based on a delay locked loop clock generated from an internal clock generator that is called a delay locked loop (hereinafter referred to as a ‘DLL’). Thus, the timing of the data strobe signal has a different value depending on the environments of a DLL block and the related circuits. The environments may include a process, voltage, and temperature (PVT).
Accordingly, semiconductor memories mounted on a module have a difference in the parameter ‘tDCSCK’.
When a dynamic random access memory (DRAM) is used as a component in a specific memory system, pieces of information are exchanged on the assumption that a data signal and a data strobe signal are reached within a given specification. Accordingly, when receiving the data signal and the data strobe signal from the DRAM, a memory controller has to secure a margin so that a normal operation is performed irrespective of whether the data signal and the data strobe signal are located at which place of a window.
As described above, since the parameters may be changed by the environments, it is required to check the AC parameters, especially clock-based parameters, to have proper values and to perform lots of tuning works, called training. However, the training requires many times of information exchanges to be taken.